1. Field of the Invention
This invention relates to transmission housing, and, more particularly, this invention relates to a modular housing design and means for providing shafts of equal length in a front housing portion and a rear housing portion to reduce shaft deflections and decrease bearing loads.
2. State of the Art
Typically, in large non-range transmissions for heavy duty trucks have two piece main shafts and countershafts because shaft deflections and bearing loads would become unmanageable with single shafts due to overall shaft length and bearing span. A past practice has been to use a separate front and a separate rear transmission case, splitting the shafts between the two cases and mounting bearings at the rear wall of the front transmission case. Unfortunately since the cases are not of equal length, the shaft sections are not equal, again resulting in excess shaft deflection and bearing loads, requiring the use of larger diameter shafts in the larger span and higher capacity bearings. This adds cost and weight to the transmission.
Where a line of transmissions are offered, even with common spacing between main shaft and countershaft but with different torque ratings and speed versions, each transmission must be built with a different single case or different front and rear cases. For example, a five speed and a seven speed without range gearing and a nine or ten speed version using a two speed range gear set all must be separately built.